The Organization for Security and Cooperation in Europe (OSCE) in Ukraine has expressed "regret" after photos appeared online showing two of its staff at the wedding celebrations of the daughter of a pro-Russia separatist in Ukraine.

One of the images shows an unidentified OSCE monitor -- employed to be an impartial observer "to contribute to reducing tensions and fostering peace, stability and security," in the words of the OSCE website -- being embraced by the separatist, Volodymyr Tymofeyev.

Yevhen Spirin, a journalist for Ukraine’s Hromadske TV, published the photos, taken from VKontakte screenshots, on his Facebook page on April 6.

Among the guests at the June 2015 wedding of Anastasia Bessedina, Tymofeyev's daughter, were the OSCE monitor and his translator.

The Luhansk and neighboring Donetsk regions were a hotbed of fighting once separatism-fueled violence broke out in April 2014, and swaths of both areas remain in Russia-backed fighters' control since a shaky truce went into effect last year.

Another image shows Tymofeyev himself (left) hugging the OSCE monitor and smiling for the camera.

After Shirin’s post was shared more than 700 times on Facebook, the OSCE Special Monitoring Mission (SMM) confirmed the photos but insisted that the monitors were not actual guests at the celebrations.

“The OSCE SMM regrets the incident. Even though the monitors did not attend the wedding as such, the photo clearly shows misjudgment on their part. These monitors are no longer with the Mission,” OSCE wrote on its official Facebook page on April 7. “The unprofessional behavior displayed by the monitors in the picture is an individual incident that should not be abused to cast a shadow on the reputation of other mission members.”

In an e-mail to RFE/RL’s Current Time, a representative for the Special Monitoring Mission press service said the monitors had been passing by the main square where members of the wedding party were taking photos. They stopped by to chat with the people with whom they were later photographed.

The press service added that they could not disclose personal information about when or under what circumstances the monitors left the Mission.

Timofeyev recently had a falling out with the separatists who currently control part of the Luhansk Oblast.

Ihor Plotnytsky, leader of the Luhansk People's Republic separatist group that opposes Kyiv and controls part of the region, accused Timofeyev of looting, rape, kidnapping, torture, and murder in Stakhanov. According to Ukrainian media, separatists arrested him and several members of his battalion in March.

OSCE monitors have been accused by both sides of bias during the conflict in eastern Ukraine, which followed Russia's covert occupation and annexation of Crimea in early 2014.

Spirin, the Hromadske journalist, expressed outrage.

“I want to ask, is OSCE an independent mission? This crap is trampling my lawns, kills my neighbors and I am supposed to read their reports?” he wrote.